Nonwoven webs with useful properties can be formed using the meltblowing process in which filaments are extruded from a series of small orifices while being attenuated into fibers using hot air or other attenuating fluid. The attenuated fibers are formed into a web on a remotely-located collector or other suitable surface.
More recently, the literature in this field has described how secondary flows of fluid can be directed onto the fibers after they have been extruded from the orifices and attenuated, but before they have impacted on the collector. By manipulating the velocity and temperature of the secondary flows, the properties of the fibers, and thus the nonwoven web they form on the collector, can be modified in useful ways.
However, there are limitations to the use of secondary flows in this way. As the rate of fabric formation is increased, at a certain point the known techniques break down. The streams of attenuating fluid and the streams of secondary fluid begin to interact in unwanted ways as production rates increase. One particular failure mode that begins to manifest is the appearance of swirling recirculation zones downstream of the orifices. Some of the emerging fibers are swept into the recirculation zones and are swept off in unwanted directions, causing waste, reducing production, and fouling equipment. There has been an ongoing effort to improve the uniformity of nonwoven webs. The art desires a mechanism by which the advantages of a secondary flow for the fiber properties can be extended to the high production rates that reduce the costs of production.